of the present-day Earth. The outer layer of ice, covered with
snow, reflects the incoming solar radiation more effectively than
land or open water. Thus, a situation is created where only a small
amount of energy is able to penetrate into the surface water or
the underlying land. Once these polar ice-caps are established,
they have the tendency to act in a self-perpetuating manner.
The freezing of sea water itself creates a form known as sea-ice.
When sea water freezes, the salts concentrate into small brine droplets
that are trapped within the ice. These brine droplets become more
saline and the freezing point of the droplets becomes greatly depressed
in comparison to that of the ice surrounding the droplets. Therefore,
the brine droplets will remain in the liquid form at temperatures
well below that of the ice formation.
Icebergs make up another major form of ice in the oceans. Icebergs
in the Arctic are carried to sea by valley glaciers from land masses
such as Greenland. These icebergs come in irregular shapes as they
are remnants of thick ice sheets that fringe on the Arctic Ocean.
The icebergs in the Southern Ocean are tabular icebergs which are
formed by the calving of the ice-shelves found in the Ross and the
Wedell Seas.
Sea water itself is very different from freshwater. Two of the
most important properties of sea water are temperature and salinity,
the concentration of dissolved salts. The two properties work in
conjunction to control the density of the water. The density of
water is a major factor which controls the vertical movement, via
condensation, of the ocean waters. The salinity of sea water is
the most important factor in the consideration of human use. The
average salinity of sea water is 35 part per thousand by weight
(3.5 percent by weight). The major ions that make up 99.9% of sea
water are as follows: |
